As is known, the skin reacts sensitively to the sun's rays, which can cause common sunburn or erythema, and also more or less severe burns.
However, the sun's rays also have other adverse effects: they cause the skin to lose its elasticity and develop wrinkles and thus lead to premature ageing. Dermatoses can also sometimes be observed. In the extreme case, skin cancer occurs in some people.
It is also desirable to protect hair from photochemical damage, in order to prevent changes in color shades, bleaching or damage of a mechanical nature.
It is known that the components contained in cosmetic preparations are not always sufficiently stable to light and decompose under the action of light rays.
As is known, ultraviolet rays with a wavelength of less than 400 nm form the most dangerous part of the sun's rays. It is also known that because of the presence of the ozone layer of the earth's atmosphere, which absorbs some of the solar radiation, the lower limit of the ultraviolet rays which reach the earth's surface is about 280 nm.
It thus appears desirable to provide compounds which can absorb UV rays in a wavelength range of 280 to 400 nm, that is to say also UV-B rays with a wavelength of between 280 and 320 nm, which play a decisive role in the development of a solar erythema, and also UV-A rays with a wavelength between 320 and 400 nm, which tan the skin but also age it, promote initiation of an erythematous reaction or intensify this reaction in certain people or can even induce phototoxic or photoallergic reactions.
The sunscreen filters nowadays customary in cosmetics are classified into UVA and UVB filters. While there are good filters in the UVB range (280-320 nm) with substances such as EUSOLEX.RTM. 6300 or EUSOLEX.RTM. 232, those used in the UVA range (320-400 nm) present problems:
Dibenzoylmethanes, such as PARSOL.RTM. 1789 or EUSOLEX.RTM. 8020, do not have an unlimited stability when exposed to UV irradiation, which on the one hand reduces the effectiveness of the filter in the course of time and on the other hand can promote photosensitizations of the skin in isolated cases. The benzophenones also used as UVA filters have only a limited solubility in the oils used in cosmetics, and they have a relatively low absorption. On the other hand, only a few water-soluble UVA filters are currently known, but their UV absorption is low.
It is known from German Reichspatent No. 676/03 that similar benzimidazole derivatives can be used as radiation protection agents, but the compounds described therein merely contain methyl or methoxy substituents. Some of those to be used according to the invention as light protection filters are known (for example DE-A 35 33 308) and some are new.